Field of the Invention
The present invention is directed to an apparatus for detecting a short-circuit in a coil of an electric motor such as a switched reluctance motor.
Japanese Patent Laid-open Print No. Hei. 10-42586, which was published on Feb. 13, 1998 without examination, discloses a driving circuit for a brush-less motor. In this driving circuit, upon detection of a continuous excess current flow through a coil for a determined time duration, such a continuation of the excess current flowing is regarded as an abnormal condition which makes the driving circuit stop the motor. Thus, in the event of a short circuit in a coil which causes an excess current flowing through a coil which is similar to the above, the motor is made to stop.
However, the foregoing concept cannot be applied to another type electric motor such as a switched reluctance motor. In detail, particularly, the switched reluctance motor includes a rotor angular position detecting sensor, a plurality of phase coils provided on a stator, a plurality of current sensors which sense the amount of current in the respective phase coils, and an energizing controller. In the energizing controller, on the basis of a target rotational number and the torque of the motor, an energizing initiating rotor angle, a de-energizing terminating rotor angle, and a reference current amount are calculated for each phase coil. When each rotor angular position detected by the corresponding rotor angular position sensor becomes the energizing initiating (energizing terminating) rotor angle position at the corresponding phase coil, the phase coil begins to be energized (de-energized) and between the energizing time point and the de-energizing time point a continual comparison is made between the detected current by the current sensor and the reference current amount for establishing a current supply control wherein if the former is less than the latter or not, the energizing remains unchanged or is stopped, respectively.
In the energizing control in the aforementioned switched reluctance motor, the current to be passed through the phase coil is to be adjusted to the reference current amount, whereby even if a short-circuit occurs in any one of the phase coils, the resultant excess current flowing through the corresponding phase coil is adjusted to the reference current amount and therefore cannot be detected. This means the concept taught by the foregoing Japanese Reference cannot be employed in switched reluctance motors.